Speed control means

ABSTRACT

IN A ROTATIONAL SPEED CONTROL MEANS FOR HAND SUSTAINED PRESSURE FLUID DRIVEN GRINDING, DRILLING AND LIKE MACHINES, PREFERABLY FOR DENTAL WORK, AN UPPER LIMIT IS PUT ON THE NUMBER OF REVOLUTIONS PER MINUTE OF THE MACHINE FROM IDLING AND UP TO FULL WORKING LOAD BY A CONTROL VALVE AND A CONTROL CIRCUIT COOPERATING TO DIVERT OR TO THROTTLE PRESSURE FLUID IN THE CONTROL VALVE IN ADVANCE OF THE MACHINE SUCH AS TO MAINTAIN AUTOMATICALLY UNDER ANY PARTIAL LOAD A PREDETERMINED SELECTIVE UPPER ROTATIONAL SPEED LIMIT FOR THE MACHINE.

- March 2, 1971 ETAL 3,567,330

SPEED CONTROL MEANS Filed Aug. is; 1969 she ts-shet 1 5 /719 0 n g .122I8 7 f v 2 March 2, 1971 APELSKOG ETAL 3,567,330

SPEED CONTROL MEANS Filed Aug. 18 1969 2 Sheets-Sheet Fig.5

fa/6% M United States Patent F 3,567,330 SPEED CONTROL MEANS Ulf MartinChristian Apelskog, Trollbacken, and Lennart Erik Idoft Gidlund,Tullinge, Sweden, assignors to Atlas Copco Aktiebolag, Nacka, SwedenFiled Aug. 18, 1969, Ser. No. 850,867 Claims priority, applicationSweden, Aug. 27, 1968, 11,529/68 Int. Cl. F01!) 25/00; F03]: 13/04; A61c1/10 U.S. "Cl. 41529 6 Claims ABSTRACT OF THE DISCLOSURE In a rotationalspeed control means for hand sustained pressure fluid driven grinding,drilling and like machines, preferably for dental work, an upper limitis put on the number of revolutions per minute of the machine fromidling and up to full working load by a control valve and a controlcircuit cooperating to divert or to throttle pressure fluid in thecontrol valve in advance of the machine such as to maintainautomatically under any partial load a predetermined selective upperrotational speed limit for the machine.

This invention relates to speed control means and more particularly torotational speed control means for hand sustained machines having apressure fluid driven rotary motor and intended for such operations asgrinding and drilling preferably in connection with dental work. In suchmachines, in the supply conduit for leading pressure fluid to the motoris usually arranged a reduction valve by which the pressure level of thepressure fluid entering the motor may be adjusted whereby the rotationalmaximum idling speed of the motor and its torque under working load areinfluenced. Often such machines are to be used with tools which becauseof the Working process or by reason of strength considerations must bedriven with low carefully limited rotational speed, such being the casefor example in special dental tools for root filling operations and ingrinding disks. Efforts have been made to limit the rotational speed forsuch special tools by lowering the pressure level by means of thereduction valve. It is true that the idling speed can be lowered in suchWay, but simultaneously the maximum torque of the tool under workingload is also lowered resulting in the lowspeed implement being unable towork satisfactorily under load.

Another measure applicable particularly in connection with grindingmachines is to provide the machine with a centrifugal regulatorcontrolling the pressure of the working fluid. This solution, however,is inappropriate in machines with very high rotational speed because ofthe usually restricted working range of centrifugal regulators and theregulator furthermore causes an undesirable increase in weight which isinconvenient particularly in dental machines.

It is an object of the invention to provide an automatically servocontrolled rotational speed control for hand sustained machines of theabove type offering an exact regulation of the rotational speed atpartial load and idling of the machine without accompanying losses inoutput torque when the tool is set under loadand without any significantincrease in weight of the machine.

For the above and other purposes there is according to the inventionprovided in a hand sustained machine for grinding, drilling and thelike, a pressure fluid driven rotary motor, a supply conduit connectedto said motor for supplying pressure fluid thereto, a pressure reductionvalve in said supply conduit for adjusting the pressure level therein,and a rotational speed control means for said machine, said rotationalspeed control means com- 3,567,330 Patented Mar. 2, 1971 prising anautomatic pressure control valve in said supply conduit between saidreduction valve and said motor actuatable for controlling the pressurebefore said motor, a servo element in said control valve for theactuation thereof, and a control circuit, said control circuit includinga servo circuit connected to said servo element for actuating saidcontrol valve, a gauging circuit for sensing the actual value of therotational speed of said motor, an adjusting circuit for adjusting therotational speed of said motor to a selective reference value lower thanthe rotational idling speed of said motor as defined by the adjustmentof said pressure reduction valve, and means in said control circuit forcontrolling through the medium of said servo element and said controlvalve the pressure before said motor such as to keep said actual valuesubstantially equal to said reference value from the instant the motorrotates idle up to the motor being under full Working load at thepressure level defined by said reduction valve.

The above and other purposes of the invention will become obvious fromthe following description and from the accompanying drawings in whichtwo embodiments are illustrated by way of example. It should beunderstood that these embodiments are only illustrative of the inventionand that various modifications thereof may be made within the scope ofthe claims.

In the drawings FIG. 1 shows a longitudinal section through the rearportion of a hand sustained machine embodying the invention. FIG. 2shows a diagrammatic longitudinal section through an automatic controlvalve embodying the invention. FIG. 3 illustrates a reduction valve forthe machine shown in FIG. 1. FIG. 4 shows an end view on the line 4-4 inFIG. 1. FIG. 5 is a partial cross section and top view of the motor inFIG. 4. FIG. 6 shows diagrammatically an electrical control circuitassociated with the automatic control valve depicted in FIG. 2. FIG. 7shows a longitudinal section through a modified embodiment of thecontrol valve. FIG. 8 is a section on the line 88 in FIG. 7.

The example chosen for description relates to rotational speed controlof a dental machine. Thus, in FIG. 1, a composite housing 10 in theshape of a hand piece is provided with a rotatably journalled drivespindle 11 which via drive axle parts 12, not shown in more detail, inknown manner drives a dental tool such as a drill, a grinding disk, orthe like, received in the machine .10. The housing 10 is provided with athrottle valve 13 inserted between a supply conduit or hose 14 and aninner chamber 15 in the machine housing 10. From the chamber 15 pressurefluid supplied through hose 14 is led via guide openings 16 against theblades 17 in a motor in the shape of a pressure fluid driven turbine 18.After the turbine 18 the pressure fluid is expelled to the surroundingatmosphere via openings 19, 20. The turbine 18 is drivingly connected tothe drive spindle 11. The throttle valve 13 is actuated manually bymeans of a lifter 21 which latter through the medium of a spring-loadedcam sleeve 22 can be displaced rearwardly in the housing 10 by a springloop 23, not shown in more detail, graspable at the forward portion ofthe housing 10, the spring loop 23 being afilxed to the cam sleeve 22.

Pressure fluid for driving the motor 18 of the machine 10 is suppliedfrom a suitable source via a hose 24, FIG. 3, to a reduction valve 25constructed in conventional way. In the reduction valve 25 is provided aball valve 27 to be opened by means of a lifter 28 against the pressureof the fluid delivered by the hose 24. The lifter 28 is loaded by aspring 30 abutting thereagainst through the intermediary of a diaphragm31, the spring 30 being adjustable as to its spring load by a knob 29.The diaphragm 31 is disposed in a chamber 32 connected by a conduit 33with an outlet conduit 34 disposed downstream with respect to the ballvalve 27. By turning of the knob 29 the load of the spring 30 is set sothat there will be maintained in the outlet conduit 34 a pressure levelreduced to the desired degree relative to the pressure level in the hose24.

Between the throttle valve 13 and the reduction valve 25 is inserted anautomatic pressure control valve 36, FIG. 2. The pressure control valve36 is connected by a hose 37 with the outlet conduit 34 of the reductionvalve 25 and includes a throttling means or aperture 38, a centralpassage 39 having a widening diifusor portion 40, and a divertingportion 42 terminated by a valve seat 41. The hose r14 of the machine 10is connected to the diffusor portion of the central passage 39. Thecontrol valve 36 is provided with a solenoid 43 which actuatesmagnetically a servo eiement 44 pivotally journalled in the controlvalve 36.

The servo element 44 has a plate-shaped portion 45 cooperating with thevalve seat 41 and rapidly adjusting itselr" relative thereto toautomatically regulated adjusting positions defined by the largeness ofthe DC. voltage energizing the solenoid 43. A piston 46 is supplied withpressure fluid from the hose 37 via a passage 47 immediately after thethrottling aperture 38. As a result the piston 46 will strive to loadthe plate-shaped portion 45 of the servo element 44 towards the seat 41against incoming fluid flow action in the diverting portion 42. With thevalve seat 41 open the pressure fluid is expelled from the divertingportion 42 via a cavity 4 8 in the control valve 36 to the surroundingatmosphere.

By numeral 50 in FIGS. 2 and 6 is designated an electrical unit boxwhich together with the automatic control valve 36 and the reductionvalve 25- is mounted separately from the hand sustained machine 10. Theelectrical unit box 50 includes the main components in an automaticcontrol circuit associated with the control valve 36.

The electrical unit box 50, FIG. 6, includes conventional transistorizedcomponents fed by a suitable voltage source, not shown. To the box 50 isconnected a gauging circuit including a conductor 51 which is extendedfrom an induction coil 52 fixed in the machine 10, in which coil 52voltage pulses are induced by permanent magnets 53 carried by theturbine 18. In the electrical unit box 50 the conductor 51 is connectedto an amplifier 54 in which the weak voltage pulses from the inductioncoil 52 are amplified for then being fed into a rectifying andintegrating block 55, the output signal of which repre sents a DCvoltage value proportional to the actual rotational speed of the motor18. This direct current voltage value represents the actual value in thecontrol circuit of the pressure control valve 36.

In the electrical unit box 50 is furthermore included an adjustingcircuit 56 in which an adjustable potentiometer 57 fed by suitable DC.voltage forms the main part. By the potentiometer there is set a DC.voltage value which in the control circuit represents the desiredreference value for the rotational speed. The actual value and thereference value are fed in the form of DC. voltage values into acontrolling means consisting of a servo amplifier 58 working as anintegrating operational amplifier in which the actuai value and thedesired value are compared over resistances 59, 60 placed in series andan output signal defined as to its polarity and largeness is producedwhich is fed into a power amplifier 61. From the power amplifier 61 theoutput signal in the form of a DC. voltage is led over a conductor 62 tothe solenoid 43 of the control valve 36 for actuation of the servoelement 44.

In use of the equipment according to FIGS. 1-6 the pressure reductionvalve 25 is set to a pressure level resulting in a certain maximaiidling rotational speed and the desired torque under full working load,respectiveiy. When automatic rotational speed control is undesirable dueto the use of sufiiciently strong tools, the reference value is set tomaximum at the potentiometer 57 which results in the servo element 44keeping the valve seat 41 closed and the pressure level in the hose 14to the machine 10 becoming substantially equal to the level adjusted atthe pressure reduction valve 25.

If it now is desired to drive use the machine with a tool which is to bestrictly limited as to the idling rotational speed thereof, it would bepossible to bring down the idling rotational speed by a substantialreduction of the pressure level in the reduction valve 25. However, withload on the tool, the low pressure level would result in a drivingtorque which normally would make effective use of the tool impossible.Therefore the servo circuit is actuated by setting by means of thepotentiometer 57 and the adjusting circuit 56 as a reference value acalibrated voltage value which puts an upper limit on the idlingrotational speed. The pressure reduction valve 25 is maintained on thepressure level which is necessary for giving sufficient torque underworking load. When as a resuit of the high pressure level the rotationalspeed during idling strives to exceed the speed limit set by thereference value, the increase in voltage coming in from the gaugingcircuit 51, 52 and and corresponding to a beginning increase of theactual value of the rotational speed of the motor 18, is received in theservo amplifier 58, the latter delivering an. output signal via theconductor 62 which as to its polarity and largeness is adapted to adjustthe servo element 44 by means of the solenoid 43. Such adjustment causesa diversion of pressure fluid from the central passage 39 in thepressure control valve 36 so that the pressure before the machine 10 isregulated during idling and thus the rotational speed is controlledtowards taking the adjusted rotational speed reference value. As soon asa load is applied against the tool, the

. rotational speed tends to 'be reduced which is counteracted by theservo element 44 successively closing the valve seat 41 more and moreuntil full closing has been reached, whereupon the machine continues towork under overload on the pressure level to which the pressurereduction valve 25 is adjusted.

In the FIGS. 7, 8 is shown a modification of the pressure control valve.The control valve 36 in question is provided with a solenoid 65 which isfixed to a throttling valve body 66. The throttling valve body 66projects into a chamber 67 set in between the hoses 37, 14 forthrottling therein the flow area when on the basis of voltage receivedin the solenoid 65 the pressure is to be influenced in the hose 14.

It should be observed that the above described adaptation to dentalmachines is only to be considered as an example and that rotationalspeed control according to the invention also is adaptable with othertypes of machines intended for grinding, drilling and like operationsand having pressure fluid motors. Such motors may be of other than ofturbine type.

What is claimed is:

1. In a hand sustained machine for grinding, drilling and the like, apressure fluid driven rotary motor, a supply conduit connected to saidmotor for supplying pressure fluid thereto, a pressure reduction valvein said supply conduit for adjusting the pressure level therein, and arotational speed control means for said machine, said rotational speedcontrol means comprising an automatic pressure control valve in saidsupply onduit between said reduction valve and said motor actuatable forcontrolling the pressure before said motor, a servo element in saidcontrol valve for the actuation thereof, and a control cir= cuit, saidcontrol circuit including a servo circuit connected to said servoelement for actuating said control vaive, a gauging circuit for sensingthe actual value of the rotational speed of said motor, and adjustingcircuit for adjusting the rotational speed of said motor to a selectivereference value lower than the rotational idling speed of said motor asdefined by the adjustment of said pressure reduction valve, and means insaid control circuit for controlling through the medium of said servoelement and said control valve the pressure before said motor such as tokeep said actual value substantially equal to said reference value fromthe instant the motor rotates idle up to the motor being under fullworking load at the pressure level defined by said reduction valve.

2. A machine according to claim 1 in which said control circuit iselectrical and said gauging and adjusting circuits thereof are connectedto feed said controlling means with electrical DC. voltage valuescorresponding respectively to said actual value and to said referencevalue, said controlling means including an integrating operationalamplifier for delivering a DC. output signal to actuate said servoelement of said control valve.

3. A machine according to claim 2 in which said gauging circuit includesinductive voltage pulse gauge means consisting of permanent magnetsarranged on said motor and cooperating with induction coil means in saidmachine, said coil means forming part of said gauging circuit.

4. A machine according to claim 3 in which said supply conduit of saidmotor is a supply hose connected to said machine, said gauging circuitincludes an amplifier separate from said machine, and said inductioncoil means is connected to said amplifier through the medium of aconductor extended through said supply hose.

5. A machine according to claim 2 in which said control valve includes avalve seat connected to said supply conduit and to passage means fordiverting pressure fluid from said supply conduit, and in which saidservo element includes a valve body cooperating with said valve seat forcontrolling fluid diversion through said passage means, and solenoidmeans for actuating said valve body.

6. A machine according to claim 2 in which said servo element includes athrottle valve body in said control valve actuatable for throttlingfluid flow through said supply conduit, and solenoid means for actuatingsaid throttle valve body.

References Cited UNITED STATES PATENTS 2,433,874 1/ 1948 Varian 415-503X3,231,237 l/1966 Wermstrom 415-503X 3,384,344 5/1968 Sadayasu Ota4l5--503X 3,472,323 10/1969 Hall 173-463 3,475,106 10/ 1969 Arneson etal 415-503X LEONARD H. GERIN, Primary Examiner US. Cl. X.R.

3227 (disc.); 415-503

